The brain uses molecules in different ways for different circumstances. Neurotransmitters are located at nerve endings and are released into synapses when an electrical signal is sent to these nerve endings. The gap between nerves, known as a synapse is too wide for the electrical signal to cross. Instead packets of molecules are released into these synaptic spaces between cells and cross these spaces to connect to specific receptors on the cell membranes on the far side of the synapse. This causes an electrical signal to be generated and sent down nerve shafts (axons and dendrites) to keep this process going.

This animation shows that when nerves fire electrically there is are interim steps that must occur at nerve interfaces call synapses. Electrical signals do not jump from one nerve to another. First the incoming nerve ending must manufacture molecules called neurotransmitters. These are brought to nerve endings and enclosed in membranes known as vesicles. These vesicles fuse with nerve membranes and release the neurotransmitters into the synaptic space between nerves, where the neurotransmitters attach to receptors on the post-synaptic nerve endings and cause the nerve to fire an electrical signal down its long shaft, known as its axon.There are multiple types of neurotransmitters with many of them serving more than one purpose. There are neurotransmitters that speed things up and those that slow things down. There are neurotransmitters that affect movement and those involved in sleep. There are neurotransmitters involved in pain and in mood, as well.

Many of the neurotransmitters involved in pain and mood are shared. The most important ones are Substance-P, norepinephrine and serotonin, but also may include GABA and Glutamate, dopamine and histamine. With all of these neurotransmitters in common, it makes sense that pain and mood are regulated together by the brain. Furthermore, these neurotransmitters have effects upon the cells, hormones and even genes. They cause further neuroplastic changes in the brain and body that can keep a pain state going or resolve it.